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  Java Practices -> Get database connection
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<div class='page-title'>Get database connection</div>

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<br>There are two sources of database connections - either a 
<tt><a href="http://java.sun.com/javase/6/docs/api/javax/sql/DataSource.html">DataSource</a></tt>
or a 
<tt><a href="http://java.sun.com/javase/6/docs/api/java/sql/DriverManager.html">DriverManager</a></tt>.

<p>If available, JNDI and the <tt>DataSource</tt> interface should
be used to get a <tt><a href="http://java.sun.com/javase/6/docs/api/java/sql/Connection.html">Connection</a></tt>
instead of <tt>DriverManager</tt>. The JNDI style is typical when using
an application server or a web container. (For example, the popular <a href="http://jakarta.apache.org/tomcat/">Tomcat</a>
product includes JNDI services and connection pools.)

<p><span class='highlight'>Always remember that database connections need to be properly released!</span>

<p>Options for specifying the connection parameters include :
<ul>
<li>
server configuration settings (likely the most common style)</li>

<li>
direct user input for user name and password</li>

<li>
a properties file, web.xml file, or <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/ResourceBundle.html">ResourceBundle</a></tt>
to keep parameters out of compiled code</li>

<li>
the <tt>jdbc.drivers</tt> property of the <tt><a href="http://java.sun.com/javase/6/docs/api/java/lang/System.html">System</a></tt>
class</li>
</ul>
<b>Example</b>
<p>Here is a reminder of the basics of getting a <tt>Connection</tt>.
<br>
<PRE>

<span class='keyword'>import</span> java.sql.*;
<span class='keyword'>import</span> javax.naming.*;
<span class='keyword'>import</span> javax.sql.*;

<span class='keyword'>final</span> <span class='keyword'>class</span> GetConnection {

  <span class='comment'>/** Uses JNDI and Datasource (preferred style).   */</span>
  <span class='keyword'>static</span> Connection getJNDIConnection(){
    String DATASOURCE_CONTEXT = <span class='literal'>"java:comp/env/jdbc/blah"</span>;
    
    Connection result = <span class='keyword'>null</span>;
    <span class='keyword'>try</span> {
      Context initialContext = <span class='keyword'>new</span> InitialContext();
      <span class='keyword'>if</span> ( initialContext == <span class='keyword'>null</span>){
        log(<span class='literal'>"JNDI problem. Cannot get InitialContext."</span>);
      }
      DataSource datasource = (DataSource)initialContext.lookup(DATASOURCE_CONTEXT);
      <span class='keyword'>if</span> (datasource != <span class='keyword'>null</span>) {
        result = datasource.getConnection();
      }
      <span class='keyword'>else</span> {
        log(<span class='literal'>"Failed to lookup datasource."</span>);
      }
    }
    <span class='keyword'>catch</span> ( NamingException ex ) {
      log(<span class='literal'>"Cannot get connection: "</span> + ex);
    }
    <span class='keyword'>catch</span>(SQLException ex){
      log(<span class='literal'>"Cannot get connection: "</span> + ex);
    }
    <span class='keyword'>return</span> result;
  }

  <span class='comment'>/** Uses DriverManager.  */</span>
  <span class='keyword'>static</span> Connection getSimpleConnection() {
    <span class='comment'>//See your driver documentation for the proper format of this string :
</span>    String DB_CONN_STRING = <span class='literal'>"jdbc:mysql://localhost:3306/airplanes"</span>;
    <span class='comment'>//Provided by your driver documentation. In this case, a MySql driver is used : 
</span>    String DRIVER_CLASS_NAME = <span class='literal'>"org.gjt.mm.mysql.Driver"</span>;
    String USER_NAME = <span class='literal'>"juliex"</span>;
    String PASSWORD = <span class='literal'>"ui893djf"</span>;
    
    Connection result = <span class='keyword'>null</span>;
    <span class='keyword'>try</span> {
       Class.forName(DRIVER_CLASS_NAME).newInstance();
    }
    <span class='keyword'>catch</span> (Exception ex){
       log(<span class='literal'>"Check classpath. Cannot load db driver: "</span> + DRIVER_CLASS_NAME);
    }

    <span class='keyword'>try</span> {
      result = DriverManager.getConnection(DB_CONN_STRING, USER_NAME, PASSWORD);
    }
    <span class='keyword'>catch</span> (SQLException e){
       log( <span class='literal'>"Driver loaded, but cannot connect to db: "</span> + DB_CONN_STRING);
    }
    <span class='keyword'>return</span> result;
  }

  <span class='keyword'>private</span> <span class='keyword'>static</span> <span class='keyword'>void</span> log(Object aObject){
    System.out.println(aObject);
  }
}
 
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<div class='topic-section'>See Also :</div>
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  <a href='TopicAction693b-2.html?Id=43'>Recovering resources</a> <br>
 
  
  <a href='TopicAction12eb-2.html?Id=75'>Connection pools</a> <br>
 
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